Japanese Knotweed FAQs

By Paolo Martini on 1st May 2019 (updated: 1st September 2020)

What is Japanese knotweed?

Japanese knotweed (also known as Fallopia japonica or Polygonum cuspidatum) is a perennial herbaceous invasive plant that is a native species of Japan. Since being imported to botanic gardens in Britain during the Victorian era Japanese knotweed has spread throughout the UK and has been labelled as ‘controlled waste’ by the government. This plant grows aggressively during the summer and has the potential to grow through temporary structures (such as garden sheds or greenhouses) and can even rupture concrete.

If you suspect knotweed to be growing either on your property or on any neighbouring land, it’s important that you take action sooner rather than later. Knotweed grows in a wide variety of climates and whilst it might be easy to spot once it’s grown in full force, it can be difficult to differentiate from a number of its relatives. Positive identification should be your first priority so that you can take action against your problem.

Japanese knotweed is more than just an unsightly weed. Capable of quickly colonising a garden, it’s root systems, known as rhizomes, are incredibly hardy and have no trouble in burrowing through driveways, cracking drains and even bringing down garden sheds. These roots cannot simply be yanked out, they require professional attention in order to be successfully and completely eradicated.

What does Japanese knotweed look like?

Japanese knotweed enters several recognisable phases throughout the year, whilst treatment can take place at any time it’s typically easier to spot during the summer, as this is when the plant is most visible above ground. You’ll first spot small red-purple asparagus-like shoots growing in spring, these can grow up to 10cm a day during the summer and often grow in large patches.

Red-purple Japanese knotweed shoots

Knotweed shoots are a red-purple colour at first.

The leaves are the most distinguishable feature throughout the year. These are broad and shield-shaped with a distinctive alternating stem pattern, unfortunately there are other common plants that look like Japanese knotweeed. Both Lilac and Dogwood share similar shaped leaves. Look for small white creamy flowers and bamboo-like canes to be certain that you have a Japanese knotweed infestation, or hire a professional to survey your property.

Related: How To Identify Japanese Knotweed

Creamy white flowers of Japanese knotweed

Knotweed’s creamy white flowers are one of their distinguishing features.

What does Japanese knotweed look like in winter?

Knotweed can be difficult to spot during the winter without its recognisable leaves and flowers, which wilt and turn yellow when the weather gets colder. Its bamboo-like stems become hollow and brittle during the winter and change from a red/brown colour in autumn to a dark brown. These hollow stems soon collapse together and decompose, but the plant is still very much alive under the ground.

Dead canes of Japanese knotweed in winter

During the winter the hollow stems become brown and brittle.

How does Japanese knotweed grow?

Despite it flowering throughout the warmer months, this is not how knotweed reproduces in the UK. This invasive plant is such a problem because of its deeply embedded root system which is constituted of ‘rhizomes’. An entire infestation can manifest itself from the smallest of rhizome fragments. Construction sites, canals and railway lines are common sources of large infestations, however unknowing gardeners attempting to dig out the root can also exacerbate the problem.

Pulling out a Japanese knotweed rhizome

Rhizome root systems can be difficult to eradicate.

Related: How Does Japanese Knotweed Spread?

How do you remove Japanese knotweed?

There are many methods of removing Japanese knotweed from your land. Which one you choose will depend on the size of the infestation that you’re dealing with, how quickly you want to clear your land and if there’s any other plant life or animals that are living in the area.

Herbicide treatment is ideal for large areas that are heavily infested and do not contain any living things that are in need of protection. Stem injection of concentrated Glyphosate herbicide is a targeted solution that is more time consuming, but also more effective. Digging out the infestation with machinery is costly, but can often be the only solution for large construction sites.

The use of a root barrier is intended to halt the spread of knotweed, rather than remove it entirely, whereas screening methods can be used to sift the soil and only remove the contaminated soil. Finally, incineration is one of the most effective methods of destroying the plant, but you must ensure that you are burning the entire infestation in order to prevent the problem returning.

How much does it cost to get rid of an infestation?

A professional spraying Japanese knotweed with glyphosate

Professional herbicide spray application is one treatment solution.

The cost of removing Japanese knotweed varies greatly depending on the size and severity of your infestation. In cases where you have not been properly informed of the knotweed, or where the plant has entered your land from a neighbouring property, you might not be liable to pay for the treatment at all.

Call us today to request a survey of your land, so that we can help determine the costs of removing the infestation and whether or not you could claim compensation to cover the treatment.

How long does it take to get rid of Japanese knotweed?

Treatment can take anywhere from 6 months to several years before proving to be effective and is heavily dependant on the size and mass of your infestation. We only work with Property Care Association (PCA) accredited removal experts who are able to give you 5 or 10 year certification in regards to your knotweed treatment.

Is it possible to get rid of it yourself?

We would strongly urge you not to attempt to treat your knotweed yourself for two reasons:

  • You’re likely to not carry out an effective treatment by yourself (and could possibly make the situation worse).
  • Also, without a certified Knotweed Management Plan, a mortgage company will not offer a mortgage on a property, regardless if the problem has been treated or not.

Although there are a number of DIY knotweed treatment solutions proffered online (bleach and vinegar being the most popular), there is no evidence that any of these are as effective as hiring a professional certified team. Glyphosate herbicide solution is available to purchase at retail stores, however commercial weed control products are not as powerful as the industrial strength solutions available to professionals and you are likely to only partially treat the problem.

If you want to get rid of your Japanese knotweed organically, then you can dig the roots out manually but once more there is no guarantee that you will complete the job. Property owners seeking to do so must also adhere to strict Japanese knotweed laws regarding the removal of this controlled substance, or risk facing serious punishments.

Related: A Guide To Getting Rid Of Japanese Knotweed

How to properly dispose of Japanese knotweed

Incorrectly disposing of Japanese knotweed or allowing any rhizomes from your waste to spread into the wild can lead to a fine of up to £5,000 or a prison sentence of up to 2 years. Regardless of if you hire a professional team to help you or not, you must use a registered waste carrier to transport your contaminated soil to a licensed landfill site. You should also call the landfill before you transport the waste, as it must have the correct environmental permit to deal with the knotweed.

Is Japanese knotweed dangerous?

Japanese knotweed can prove to be an expensive, time-consuming problem to deal with, however it is not dangerous to humans. Japanese knotweed is not poisonous, in fact, it’s edible and can be consumed easiest when it’s first shooting in spring.

Should I buy a house with Japanese knotweed?

Japanese knotweed growing in a suburban back garden

Properties with knotweed present lose 10% of their value.

If you buy a property with a Japanese knotweed infestation then you are inheriting years of treatment and the costs that go with it. An infestation of knotweed typically reduces a domestic property’s value by 10%. Some mortgage lenders have specific policies regarding this plant, so it’s worth enquiring with them before committing.

A knotweed infestation should be identified by the seller of your home on the TA6 form. If you have spotted knotweed on the property, but the seller has answered ‘Not Known’ on the survey form then you should bring this issue up with them straight away. Unfortunately, in some cases, property sellers lie about Japanese knotweed in order to push through a quick sale.

Find out about what happens if you’ve bought a property with knotweed in this case study.

How about selling a house with Japanese knotweed?

Conversely, if you are aware of a Japanese knotweed infestation on your property you must make potential buyers fully aware of this by noting it on the TA6 information form. Failing to do so could lead to a lawsuit that could cost you thousands of pounds. Similarly, if a property surveyor misses Japanese knotweed on your land and a buyer makes a claim against you, you may able to claim against the surveyor for professional negligence.

Read: Selling a Property with Japanese Knotweed

What do you do if you find Japanese knotweed in your garden?

It is not illegal to allow Japanese knotweed to grow on your land, so you are not required by law to notify anyone about an infestation. However, it is certainly in your interest to deal with the problem as soon as possible.

This plant is controlled by both the Anti-social Behaviour Crime and Policing Act 2014, the Environmental Protection Act 1990 and the Wildlife and Countryside Act 1981. Whilst harbouring the plant on your property is not illegal, allowing a knotweed infestation to spread into another property is and could lead to fines and lawsuits being brought against you. Leaving the plant to grow in size will only lead to your overall costs increasing with it.

Read our guidelines to find more about the laws controlling Japanese knotweed.

Who is responsible for clearing Japanese knotweed?

The responsibility for removing or clearing the Japanese knotweed rests on the individual whose land the plant originated on. For example, if knotweed in your neighbour’s garden has spread to your land then it would be their responsibility to pay for the treatment of the infestation. In order to claim for the costs of removal, you will need to prove that the infestation came from their land.

What is the limitation period for Japanese knotweed claims?

If you are considering making a claim for damages, it is important to seek advice as soon as possible. This is because legislation requires that you must commence your Japanese knotweed claim within certain time limits after discovering its presence. After this, it will almost always be too late.

We specialise in these knotweed nuisance claims and our lead solicitor, Mark Montaldo, has advised a Parliament Select committee on the issues facing homeowners with Japanese knotweed on their land.

Get in touch with us if you have any questions about how to deal with Japanese knotweed, we work on a No-Win No-Fee agreement and never take on a case that we don’t think we can win.

Paolo Martini

Paolo Martini is the lead solicitor for Knotweed Help and has over 30 years of experience in the field of Civil Litigation and is an expert on the legal issues faced by individuals dealing with Japanese knotweed on their land. Now considered one of the country's leading litigators in Japanese knotweed law he works alongside the country’s top barristers and experts. His in-depth legal experience and connections to the Japanese knotweed removal industry make him uniquely suited for handling your case.